Fine particles in the air that contain soot or black carbon are formed as a result of incomplete combustion. Reduction of black carbon emissions is one way to mitigate climate change – but only in the short run.
Photo: Eija Vallinheimo
Alongside methane, black carbon or soot is the most important short-lived compound that affects the climate. It has been estimated that black carbon in the air accelerates climate change because it absorbs sunlight, which warms up the atmosphere. In addition to this direct effect, black carbon accelerates climate change by reducing the reflection of sunlight from ice back to the space and by accelerating the melting of snow and ice, particularly in Arctic areas.
Black carbon stays in the atmosphere from a few days to a few weeks, making its climate effects local and transient. "By reducing the emissions of black carbon, we can mitigate climate change temporarily but reduction of greenhouse gas emissions, and particularly carbon dioxide emissions, is the only way to mitigate climate change in the long run," emphasises Heikki Lihavainen, a research professor at the Finnish Meteorological Institute.
Globally speaking, the climate effect of black carbon emissions in Finland during the summertime accounts for approximately one per mille, but during winter, Finland produces one per cent of the soot that settles on snow. That makes the wintertime emissions in Finland significant. In Finland, over 50% of the total soot emissions come from residential combustion of wood. Emissions from traffic will decrease substantially because of the new emission requirements for diesel vehicles. There is no emission legislation for residential combustion of wood as of yet. That accentuates the importance of correct combustion methods, particularly in urban areas where the adverse health effects of soot particles are also more pronounced.
Black carbon emissions can be reduced significantly with existing technologies. More research on black carbon is needed, however, because in addition to fine particle emissions, we need to have a comprehensive picture of their transformation in the atmosphere before we can assess their effects on health and the environment and plan reductions and restrictions of emissions. Residential combustion of wood, for example, releases particles that cool down the climate, in addition to black carbon particles that warm up the climate. The combustion technique and material used impact the amount of these warming and cooling particles. These questions must be studied further, and they might produce surprising results on the overall effect of the reduction of black carbon emissions.
Research professor Heikki Lihavainen, email@example.com